A radio coverage map of an access point is a map of the signal strength of a signal transmitted by the access point as received at various locations on the map. Radio coverage maps of access points located in a building are important in indoor positioning. Radio coverage maps of access points located in the building are provided to a mobile station to assist the mobile station in determining its position. Using the radio coverage maps, the mobile station determines which access points to scan. The mobile station scans these access points and measures received signal strength indicator (RSSI) values from signals transmitted by these access points. The radio coverage map is also commonly called an RSSI heatmap. The radio coverage map is usually a three-dimensional radio coverage map. The radio coverage map is typically generated in advance by a server. Traditionally, the radio coverage map is generated by using the well-known dominant path model or ray tracing model.
Buildings such as malls and airports often have partial ceilings. In other words, two or more physical levels (i.e., floors or ceilings) of such building share the same top ceiling. If the partial ceilings are considered in the traditional process of generating the radio coverage maps of the access points located in such building (for example, by using the dominant path model or ray tracing model), this traditional process will require a very large amount of time and processing power. Thus, using the traditional process, it is not possible to generate quickly a radio coverage map of an access point located in such building, and it is not feasible for a mobile station, with its limited processing power, to generate a radio coverage map by itself.